Root traits and growth of spreading orach and common lambsquarters were compared in response to soil compaction, drought, and waterlogging under controlled environment conditions. On the basis of the typical habitats occupied, the hypothesis was that spreading orach would be more tolerant of compaction and waterlogging and common lambsquarters more tolerant of drought. When grown in buckets with two soil bulk densities (1.2 and 1.6 g cm⁻³) for 8 wk, the two species responded similarly to compaction, with the fraction of fine roots reduced by 10%, total root length by 70%, root and shoot dry weight and leaf area by 50 to 60%, and plant height by 30% at the high compared with the low bulk density. When grown for 6 wk in soil columns 1 m long, which were watered daily or allowed to dry, common lambsquarters was deeper rooted than spreading orach at both moisture levels and better able to sustain growth in the drying columns. The watering regime did not alter the rooting depth of either species. Total root length in successive 10-cm increments declined exponentially from the top to the bottom of the watered columns, but root proliferation was reduced in the upper 20 cm of the drying columns. The average root diameter of both species decreased with drought and increased with soil compaction. When grown in waterlogged soil at 10 or 20 C for 4 wk, seedlings of spreading orach survived with little reduction in growth, whereas survival and growth of common lambsquarters were drastically reduced, particularly under cool soil conditions.

Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; spreading orach, Atriplex patula L. ATXPA.